[Qemu-devel] [PATCH] linux-user: remove useless padding in flock64 structure

[Qemu-devel] [PATCH] linux-user: remove useless padding in flock64 structure

[Laurent Vivier]

Since commit 8efb2ed5ec ("linux-user: Correct signedness of
target_flock l_start and l_len fields"), flock64 structure uses
abi_llong for l_start and l_len in place of "unsigned long long"
this should force them to be aligned accordingly to the target
rules. So we can remove the padding field and the QEMU_PACKED
attribute.

I have compared the result of the following program before and
after the change:

    cat -> flock64_dump  <<EOF
    p/d sizeof(struct target_flock64)
    p/d &((struct target_flock64 *)0)->l_type
    p/d &((struct target_flock64 *)0)->l_whence
    p/d &((struct target_flock64 *)0)->l_start
    p/d &((struct target_flock64 *)0)->l_len
    p/d &((struct target_flock64 *)0)->l_pid
    quit
    EOF

    for file in build/all/*-linux-user/qemu-* ; do
    echo $file
    gdb -batch -nx -x flock64_dump $file 2> /dev/null
    done

The sizeof() changes because we remove the QEMU_PACKED.
The new size is 32 (except for i386 and m68k) and this is
the real size of "struct flock64" on the target architecture.

The following architectures differ:
aarch64_be, aarch64, alpha, armeb, arm, cris, hppa, nios2, or1k,
riscv32, riscv64, s390x.

For a subset of these architectures, I have checked with the following
program the new structure is the correct one:

  #include <stdio.h>
  #define __USE_LARGEFILE64
  #include <fcntl.h>

  int main(void)
  {
	  printf("struct flock64 %d\n", sizeof(struct flock64));
	  printf("l_type %d\n", &((struct flock64 *)0)->l_type);
	  printf("l_whence %d\n", &((struct flock64 *)0)->l_whence);
	  printf("l_start %d\n", &((struct flock64 *)0)->l_start);
	  printf("l_len %d\n", &((struct flock64 *)0)->l_len);
	  printf("l_pid %d\n", &((struct flock64 *)0)->l_pid);
  }

[I have checked aarch64, alpha, arm, s390x]

I have also fixed the alignment value for sh4 (to align llong on 4 bytes)
(see c2e3dee6e0 "linux-user: Define target alignment size")

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
---
 include/exec/user/abitypes.h |  2 +-
 linux-user/syscall_defs.h    | 23 ++++++++---------------
 2 files changed, 9 insertions(+), 16 deletions(-)

diff --git a/include/exec/user/abitypes.h b/include/exec/user/abitypes.h
index ba188608c2..743b8bb9ea 100644
--- a/include/exec/user/abitypes.h
+++ b/include/exec/user/abitypes.h
@@ -15,7 +15,7 @@
 #define ABI_LLONG_ALIGNMENT 2
 #endif
 
-#if defined(TARGET_I386) && !defined(TARGET_X86_64)
+#if (defined(TARGET_I386) && !defined(TARGET_X86_64)) || defined(TARGET_SH4)
 #define ABI_LLONG_ALIGNMENT 4
 #endif
 
diff --git a/linux-user/syscall_defs.h b/linux-user/syscall_defs.h
index 23f5bccf0e..df3847bc16 100644
--- a/linux-user/syscall_defs.h
+++ b/linux-user/syscall_defs.h
@@ -2649,28 +2649,21 @@ struct target_flock {
 };
 
 struct target_flock64 {
-    short  l_type;
-    short  l_whence;
-#if defined(TARGET_PPC) || defined(TARGET_X86_64) || defined(TARGET_MIPS) \
-    || defined(TARGET_SPARC) || defined(TARGET_HPPA) \
-    || defined(TARGET_MICROBLAZE) || defined(TARGET_TILEGX) \
-    || defined(TARGET_XTENSA)
-    int __pad;
-#endif
+    abi_short l_type;
+    abi_short l_whence;
     abi_llong l_start;
     abi_llong l_len;
-    int  l_pid;
-} QEMU_PACKED;
+    abi_int   l_pid;
+};
 
 #ifdef TARGET_ARM
 struct target_eabi_flock64 {
-    short  l_type;
-    short  l_whence;
-    int __pad;
+    abi_short l_type;
+    abi_short l_whence;
     abi_llong l_start;
     abi_llong l_len;
-    int  l_pid;
-} QEMU_PACKED;
+    abi_int   l_pid;
+};
 #endif
 
 struct target_f_owner_ex {
-- 
2.14.3

Re: [Qemu-devel] [PATCH] linux-user: remove useless padding in flock64 structure

[Richard Henderson]

On 05/01/2018 04:53 PM, Laurent Vivier wrote:
> Since commit 8efb2ed5ec ("linux-user: Correct signedness of
> target_flock l_start and l_len fields"), flock64 structure uses
> abi_llong for l_start and l_len in place of "unsigned long long"
> this should force them to be aligned accordingly to the target
> rules. So we can remove the padding field and the QEMU_PACKED
> attribute.
> 
> I have compared the result of the following program before and
> after the change:
> 
>     cat -> flock64_dump  <<EOF
>     p/d sizeof(struct target_flock64)
>     p/d &((struct target_flock64 *)0)->l_type
>     p/d &((struct target_flock64 *)0)->l_whence
>     p/d &((struct target_flock64 *)0)->l_start
>     p/d &((struct target_flock64 *)0)->l_len
>     p/d &((struct target_flock64 *)0)->l_pid
>     quit
>     EOF
> 
>     for file in build/all/*-linux-user/qemu-* ; do
>     echo $file
>     gdb -batch -nx -x flock64_dump $file 2> /dev/null
>     done
> 
> The sizeof() changes because we remove the QEMU_PACKED.
> The new size is 32 (except for i386 and m68k) and this is
> the real size of "struct flock64" on the target architecture.
> 
> The following architectures differ:
> aarch64_be, aarch64, alpha, armeb, arm, cris, hppa, nios2, or1k,
> riscv32, riscv64, s390x.
> 
> For a subset of these architectures, I have checked with the following
> program the new structure is the correct one:
> 
>   #include <stdio.h>
>   #define __USE_LARGEFILE64
>   #include <fcntl.h>
> 
>   int main(void)
>   {
> 	  printf("struct flock64 %d\n", sizeof(struct flock64));
> 	  printf("l_type %d\n", &((struct flock64 *)0)->l_type);
> 	  printf("l_whence %d\n", &((struct flock64 *)0)->l_whence);
> 	  printf("l_start %d\n", &((struct flock64 *)0)->l_start);
> 	  printf("l_len %d\n", &((struct flock64 *)0)->l_len);
> 	  printf("l_pid %d\n", &((struct flock64 *)0)->l_pid);
>   }
> 
> [I have checked aarch64, alpha, arm, s390x]
> 
> I have also fixed the alignment value for sh4 (to align llong on 4 bytes)
> (see c2e3dee6e0 "linux-user: Define target alignment size")

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~

Re: [Qemu-devel] [PATCH] linux-user: remove useless padding in flock64 structure

[Laurent Vivier]

Le 02/05/2018 à 01:53, Laurent Vivier a écrit :
> Since commit 8efb2ed5ec ("linux-user: Correct signedness of
> target_flock l_start and l_len fields"), flock64 structure uses
> abi_llong for l_start and l_len in place of "unsigned long long"
> this should force them to be aligned accordingly to the target
> rules. So we can remove the padding field and the QEMU_PACKED
> attribute.
> 
> I have compared the result of the following program before and
> after the change:
> 
>     cat -> flock64_dump  <<EOF
>     p/d sizeof(struct target_flock64)
>     p/d &((struct target_flock64 *)0)->l_type
>     p/d &((struct target_flock64 *)0)->l_whence
>     p/d &((struct target_flock64 *)0)->l_start
>     p/d &((struct target_flock64 *)0)->l_len
>     p/d &((struct target_flock64 *)0)->l_pid
>     quit
>     EOF
> 
>     for file in build/all/*-linux-user/qemu-* ; do
>     echo $file
>     gdb -batch -nx -x flock64_dump $file 2> /dev/null
>     done
> 
> The sizeof() changes because we remove the QEMU_PACKED.
> The new size is 32 (except for i386 and m68k) and this is
> the real size of "struct flock64" on the target architecture.
> 
> The following architectures differ:
> aarch64_be, aarch64, alpha, armeb, arm, cris, hppa, nios2, or1k,
> riscv32, riscv64, s390x.
> 
> For a subset of these architectures, I have checked with the following
> program the new structure is the correct one:
> 
>   #include <stdio.h>
>   #define __USE_LARGEFILE64
>   #include <fcntl.h>
> 
>   int main(void)
>   {
> 	  printf("struct flock64 %d\n", sizeof(struct flock64));
> 	  printf("l_type %d\n", &((struct flock64 *)0)->l_type);
> 	  printf("l_whence %d\n", &((struct flock64 *)0)->l_whence);
> 	  printf("l_start %d\n", &((struct flock64 *)0)->l_start);
> 	  printf("l_len %d\n", &((struct flock64 *)0)->l_len);
> 	  printf("l_pid %d\n", &((struct flock64 *)0)->l_pid);
>   }
> 
> [I have checked aarch64, alpha, arm, s390x]
> 
> I have also fixed the alignment value for sh4 (to align llong on 4 bytes)
> (see c2e3dee6e0 "linux-user: Define target alignment size")
> 
> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
> ---
>  include/exec/user/abitypes.h |  2 +-
>  linux-user/syscall_defs.h    | 23 ++++++++---------------
>  2 files changed, 9 insertions(+), 16 deletions(-)
> 
> diff --git a/include/exec/user/abitypes.h b/include/exec/user/abitypes.h
> index ba188608c2..743b8bb9ea 100644
> --- a/include/exec/user/abitypes.h
> +++ b/include/exec/user/abitypes.h
> @@ -15,7 +15,7 @@
>  #define ABI_LLONG_ALIGNMENT 2
>  #endif
>  
> -#if defined(TARGET_I386) && !defined(TARGET_X86_64)
> +#if (defined(TARGET_I386) && !defined(TARGET_X86_64)) || defined(TARGET_SH4)
>  #define ABI_LLONG_ALIGNMENT 4
>  #endif
>  
> diff --git a/linux-user/syscall_defs.h b/linux-user/syscall_defs.h
> index 23f5bccf0e..df3847bc16 100644
> --- a/linux-user/syscall_defs.h
> +++ b/linux-user/syscall_defs.h
> @@ -2649,28 +2649,21 @@ struct target_flock {
>  };
>  
>  struct target_flock64 {
> -    short  l_type;
> -    short  l_whence;
> -#if defined(TARGET_PPC) || defined(TARGET_X86_64) || defined(TARGET_MIPS) \
> -    || defined(TARGET_SPARC) || defined(TARGET_HPPA) \
> -    || defined(TARGET_MICROBLAZE) || defined(TARGET_TILEGX) \
> -    || defined(TARGET_XTENSA)
> -    int __pad;
> -#endif
> +    abi_short l_type;
> +    abi_short l_whence;
>      abi_llong l_start;
>      abi_llong l_len;
> -    int  l_pid;
> -} QEMU_PACKED;
> +    abi_int   l_pid;
> +};
>  
>  #ifdef TARGET_ARM
>  struct target_eabi_flock64 {
> -    short  l_type;
> -    short  l_whence;
> -    int __pad;
> +    abi_short l_type;
> +    abi_short l_whence;
>      abi_llong l_start;
>      abi_llong l_len;
> -    int  l_pid;
> -} QEMU_PACKED;
> +    abi_int   l_pid;
> +};
>  #endif
>  
>  struct target_f_owner_ex {
> 

I think my change breaks the ARM OABI: in QEMU, OABI uses target_flock64
and in  kernel it uses oabi_flock64 which uses "__attribute__
((packed,aligned(4)));".
While in kernel EABI uses the standard flock64 structure and in QEMU
arm_eabi_flock64...

Thanks,
Laurent